Obstructive sleep apnea (OSA) is a common disorder characterized by repetitive, complete, or partial collapse of the upper airway during sleep that affects at least 9% of middle-aged women and 24% of middle-aged men in the United States. The reported prevalence of OSA among patients presenting for surgery ranges from 3% in general surgery, to 70% among obese patients undergoing bariatric procedures, however OSA is often undiagnosed and the true prevalence is likely much higher. Patients with OSA have an increased risk of postoperative adverse events including respiratory failure and cardiovascular complications, increased need for intensive care unit admission, and prolonged hospitalization. The long-term treatment of OSA in the ambulatory setting consists of continuous positive airway pressure, a form of noninvasive ventilation (NIV). Based largely on the knowledge that patients with OSA are at increased risk of complications, and extrapolating from the benefits of chronic therapy, guidelines from the American Society of Anesthesiology recommend that all patients with OSA receive NIV and have oximetry monitoring for a prolonged period following surgery. Limited evidence, together with the cost and complexity of delivering NIV and providing monitoring may explain why 80% of US hospitals do not currently have policies or protocols in place for managing these patients. Using a highly detailed database containing patient records from a geographically and structurally diverse set of 400 US hospitals, our aims are to: 1) examine the use of NIV postoperatively in patients with OSA following major non-cardiac surgery and to identify patient and hospital factors associated with treatment, 2) analyze the association between treatment with NIV and postoperative outcomes in patients with OSA undergoing major non-cardiac surgery. The primary outcome of interest will be the development of serious respiratory deterioration, defined as intubation or respiratory arrest. Secondary outcomes will include other respiratory and cardiovascular complications, in-hospital mortality, length of stay, and cost of hospitalization. To limit the threat of selection bias we will employ a powerful set of analytical methods including hierarchical logistic regression, high-dimensional propensity scores, and instrumental variable techniques. Successful completion of the aims of this project will generate important new knowledge about the use of NIV in patients with OSA in the postoperative period as well as evidence about its effectiveness in routine clinical settings. These findings will either strengthen current guide recommendations, serving as a catalyst for future dissemination and implementation studies, or alternatively, will challenge them, highlighting the need for better evidence to guide practice. This proposal builds upon our team's strong record of comparative effectiveness research in perioperative medicine and will improve the treatment of patients with OSA.